Asterisk Coin Trunks

Background

Coin controllers have existed for payphones for quite some time, allowing collectors to restore old or acquired payphones to their original operation. However, this equipment is bulky, expensive, and typically inflexible.

In 2019, several telephone collectors were able to modify the source code of some DSP code in Asterisk to create detectors for MF, SF, and single-slot coin denomination tones (often erroneously known as "ACTS" tones, due to their use in ACTS coin trunks). It wasn't long before we got Asterisk to reliably detect single-slot coin denomination tones, and soon we started writing a wrapper for that which evolved into the ongoing NPSTN coin trunks project.

How it works

A centralized NPSTN tandem is set up with emulation for several kinds of coin trunks. At this time, this includes single-slot coin first (prepay), post pay (Western Electric style), dial-tone first pre-pay, as well as ACTS. The first three trunks are essentially complete, and we are working on the ACTS trunk as well as final touches.

The coin trunks are all emulated fully on a remote Asterisk system, which means the owner does not need to be concerned about the details of the trunk operations himself. All he needs to do is have his payphone automatically dial (using an ATA, channel bank, or directly from within his local Asterisk box) to the appropriate coin trunk. These trunks are fully integrated into the NPSTN mock toll ticketing system, so calls made will appear appropriately on the bill associated with the coin phone.

What needs to be done

We still need to include support for collect and return. This is one reason coin controllers are often used - interfacing 130 V AC with your phone is no easy or trivial task. However, it can be done, and much more cheaply than efficiently than using dedicated coin controller equipment.

We are working on designing custom equipment that will be cheap and easy to mass-produce, which will include the ability to detect MF tones from the remote coin trunk. This equipment would go between the payphone and its associated line equipment (ATA/channel bank, etc.) and would allow for local voltage operations which require a physical connection to the phone.

Finally, in the future, we hope to expand this to 3-slot coin phones as well. One additional barrier here is the reliable and accurate detection of the 3-slot gongs, which is an issue we are studying at the moment extensively.

How YOU can help

If you have suggestions on 3-slot coin detection or voltage control, we'd love to hear from you! Please leave a comment below.